Please help me diagnose this kaboom...

[Zradix]

Working on my first trilam.
I was just getting it to a low brace.
I had to get the midlimbs moving a lot to get the tips into position.
Things were looking very good. no obvious hinges..other than the midlimbs were bending a lot more than the rest to bring the tips around.

The break was instant. No pops, creaks nothing..just pow.
The woods are hickory back, walnut core, osage belly.
I noticed the hickory didn't splinter at all. Just broke pretty clean as the pics will show.

I purposely broke a small piece of hickory that I had and it broke the same way. Is it normal not to splinter?

Noticed the osage is the only lam that didn't break through.

Here are my thoughts...
The design may be more than wood can take period.

The backing may have just gave way..too much pressure in too small an area.

The walnut being much thicker than than the belly or back was actually doing too much work and broke. Just too thick to bend that much.

I'm leaning towards the core being too thick for the amount of flex.
Maybe walnut just doesn't bend like that...too brittle?

If the core is what gave... I'm pondering the notion of using 2 thinner core layers and/or a different material..maybe action boo.

Here the pics..
Let me know what ya think..
Thanks.    

Here's the unbraced profile...you can see how the mid limbs needed to go a long way to get to a braced position...
 

Here's the breaks..
 

 

 

[fujimo]

just looking at it, and seeing how far the mid limbs had to move- and no splinters-looks like it just pulled the hickory apart.
seems like there might be something amiss with that hickory, can you clamp that bow in a vice. and pull on the other limb( with a rope from a safe distance) and see what happens to it.- maybe video it!?!

[Echatham]

If you had the mid limbs bending more than another part wouldnt that be a hinge?  Even though it may still be reflexed at a point of the draw?

[Zradix]

That was my thought too Eric.
But I don't know of any other way to make the tips come around for brace. I'm fully open to the idea that this bow was just too curvy.

[Echatham]

Sorry double post.  Maybe that design would require the string to lay against the belly at brace like a recurve

[Roy from Pa]

You needed to facet the Osage belly right to the glue joint between the Osage and walnut. Your belly edges are too square. I round the belly off to a radius belly. Also there is a hinge where the belly was too thin.

[Bowjunkie]

You should not have thinned the midlimb to "get the limb tips to come around". Doing so made it weaker there than elswhere, and I think it's obvious now why that should be avoided. If it was too strong to get it braced, you should have reduced it's strength by removing wood evenly along the limbs' length in thickness and/or width while maintaining an even thickness taper.

I would have been especially meticulous about the thickness tapering of the limbs. As long as it is accurate, the bow will try to reveal to you what its basic strung profile should look like. Listen to her. Go with her. Don't try to make her something she's not.

With that unstrung profile, it would likely want to show a braced profile that still shows some reflex. Following that, it will then show the limbs straight at partial draw, and "come around" sometime a little later in the draw... but never come around as much as a straight limbed bow.

A common mistake of folks who are new to d/r bows is trying to make their profiles resemble those that stand straight or with gentle reflex when unstrung.

[Bowjunkie]

I have one going now that looks much like it. It is just now ready for the tree... hasn't been bent at ALL yet. I'll take pictures when I get to working on it again... not sure when that will be though  :(

[Roy from Pa]

John, when tillering these d/r bows, you want the entire limb to bend a little. The last thing that should be bending is the area just outside of the dips. As you pull the bow down, watch the limbs. Look to see where it is flexing. If all the bend is at the end of the riser, then that is not good. You need to watch the limbs as they react when pulling the bow on the tree. The heavy reflex in your bow is going to make those outer limbs really stiff. Even at full draw they will still hold some reflex. At a brace the mid limbs will be pretty straight looking. As you work it down the tree, the mid limbs should begin to bend, and some of the reflex will come out, but not all of it, and at the end of the riser you don't want the limb bending at all. That area will take on some bend as you get farther down the tree. It's hard to explain, but think about it like a wave rolling in on the ocean. Take a wooden yard stick and hold it at arms length, then bend both ends down, it will have an even arc. Add in the reflex and the outer 1/3 third of the limbs will still be reflexed. But most of all when pulling the bow on the tree, see how it's bending. It should be an equal bend so to speak along the entire limb, Not one area bending like a door hinge. I know, this doesn't help:)

[Zradix]

Good luck Jeff!

Thanks for the help guys.
I understand what you guys are saying.
Maybe I did try to force it.
In some ways I feel like I was pretty close to a good brace profile....following the ideas you've posted.
..in others memory says the mid limbs were bending too much.

I think part of the problem may be the unbraced profile.
when you really look at it, the midlimbs are about the only place in the limb that's really curved. Sure the outer libs have some but not much. Almost like 2 straight lines with a curve in the middle.

If I made the entire limb bend the same amount throughout it would have weird belly pointed tips and fades with this odd bump in the middle of the limb.

I think it would really help to have a more gentle arc through out the limbs.
This one was glued up with a profiled back, but the core and belly were still just rectangular slats.
If I would have profile tapered the core and belly it would probably have a more even arc....hhhmmmm

I really appreciate you all talking this out with me and letting me bounce around ideas.
   

[Pat B]

The only time I've seen hickory break in tension across the grain the hickory was infected with fungi. If it were healthy is would have splintered more.

[Zradix]

How can you tell infected hickory?
Not saying this was in particular, but it would be nice to know.

[Roy from Pa]

John, I really think for you not making many bows, you induced way too much deflex and reflex. If you remember in your other thread, a few Bowyer guys said good luck tillering that thing. Deflex and reflex is nice, but too much is not a good thing either for someone who has not made many bows. That's my final answer:)

[Zradix]

yep..
I agree.
Was a real eye opener.
also realized with actual experience how much more touchy keeping the limbs straight is when there's so much bend in them.
I've heard it was...but how much worse could it be right...lol

Still want to try to make a trilam....even worse now. like it to be made from 62" lams. can that be done in a mild r/d bow and still get 28" draw w/o too much stack?
I realized this year that I really didn't like hunting with such a long bow.

[Roy from Pa]

There won't be no stack.

[Zradix]

ok.
Guess the drawing board is coming back out.

[Pat B]

Zradix, Just the fact that it broke across the grain tells me there is a problem with the hickory. Hickory is very strong in tension and not apt to break across the grain.
  I've made lots of hickory backed bows and the only one that failed was due to fungi in the wood.

[Black Mockingbird]

I agree with everything pat,Roy,and Jeff has told you...I think your hickory is bad and if u have some of the same stuff left do some bend tests with it first before wasting anymore time with it...if the hickory is bad then no matter what shape or design you do its gonna blow...So find out first if its any good...I'm betting it isn't..as pat said its bad hickory that breaks straight across like that and good hickory will splinter...and the other problem is as Roy n Jeff says...too extreme of a shape for a novice to handle...and honestly I didn't like the shape of it having all the reflex in one small area so closer to the fades than the tips....try getting your reflex to start mid limb and then continue it progressively more in one sweeping arc to the tips...and getting your lams perfectly thickness tapered will aid in this...I dont think you thickness tapered your lams good enough on that one because all the bend happened in that one area during glue up...

[Bowjunkie]

Exactly, precision tapering PRIOR to glue up is a key move on bows like this. I grind mine as precisely as I grind glassbow lams, and when ya pull it down into reflex on the form, not only is the reflex evenly distributed during glue up, the dang thing pertinear tillers itself.

I saw this mentioned earlier... I DON'T have the pieces shaped at all in regards to their width profiles prior to glue up. Doing so would limit room for shifting centerline during layout. The exception to this is bamboo backing... I shape it to oversized width profile so it can be adequately thinned... since it is so high-crowned.

[Zradix]

I agree with all of ya.

I know the biggest failure here is me.

Maybe the hickory was bad. I had one little 8" or so piece that came with the lams...for packing I think. Looked exactly like the backing.
That little piece broke w/o splinters...broke exactly like the backing.

I'm pretty sure the lams were evenly tapered. I may not have specified the right amount of taper, but I'll bet they were evenly tapered.  Don't have the specs right here..but the backing was tapered 1/8 to 1/16", the core was .004 taper, the belly was .003. ( may have those flipped around) They had a 14.5" parallel center section.

Thanks for the help guys.    

Can you tell if hickory is bad by looking at it?